Olivier Dewitte

Royal Museum for Central Africa · Department of Earth Sciences

Proceedings of the 7th International Geologica Belgica Congress: 15-17 September 2021 – Africamuseum Tervuren (Belgium) - Geosciences made in Belgium. The Royal Museum for Central Africa was pleased to welcome the 7th international Geologica Belgica Meeting 2021 in the recently renovated AfricaMuseum. Modern conference rooms and facilities within...

Like many other lakes in the world, the interconnected Abaya and Chamo lakes in the Southern Main Ethiopian Rift are affected by rapid sediment accumulation. Although land degradation is a well-known issue in this part of the African continent, the main sediment sources, their spatial distribution and interaction in the Abaya–Chamo lakes’ basin hav...

Like many other lakes in the world, the interconnected Abaya and Chamo lakes in the Southern Main Ethiopian Rift are affected by rapid sediment accumulation. Although land degradation is a well-known issue in this part of the African continent, the main sediment sources, their spatial distribution and interaction in the Abaya–Chamo lakes’ basin hav...

Landslides and flash floods are geomorphic hazards (GH) that often co-occur and interact. They generally occur very quickly, leading to catastrophic socioeconomic impacts. Understanding the temporal patterns of occurrence of GH events is essential for hazard assessment, early warning and disaster risk reduction strategies. However, temporal informa...

The mountainous environments of the Northern-western provinces of Rwanda are often affected by severe cases of rainfall-triggered landslides. Recent studies carried out in the region reveal that the peak in the occurrence of these new landslides is not associated with the highest monthly rainfall, but occurs at the end of the wet season when the an...

Spatio-temporal inventory of natural hazards is a challenging task especially in rural or remote areas in the Global South where data collection at regional scale is difficult. Citizen science, i.e., involvement of no-experts in collecting information and co-creation of knowledge with experts to solve societal and environmental problems, has been s...

Disasters related to hydrological hazards are frequent, occur worldwide, and regularly devastate many African cities. The victims are commonly among the population in precarious situations, without solid infrastructure and with incomes too low to recover from disasters. Located in the western branch of the East African Rift, and squeezed between th...

Uvira is a rapidly growing city of about 600,000 inhabitants in DR Congo. Squeezed between the shore of Lake Tanganyika and steep mountains hillslopes, and under the influence of a tropical climate, the city is familiar with flash floods. Nevertheless, the impacts of the flash flood event of April 2020 have been unprecedented in the last decades. D...

Tropical environments favour chemical weathering and regolith development. Weathering induces textural, mineralogical and chemical changes in rocks, modifying their strength and thus affecting slope stability. Degree of weathering is, however, not only a function of climatic conditions, but is also influenced by e.g. bedrock composition and structu...

The Rwenzori Mountains, in southwest Uganda, are prone to precipitation-related hazards such as flash floods and landslides. These natural hazards highly impact the lives and livelihoods of the people living in the region. However, our understanding of the precipitation patterns and their impact on related hazardous events and/or agricultural produ...

Tropical mountainous regions are often identified as landslide hotspots with particularly vulnerable populations. Anthropogenic factors are assumed to play a role in the occurrence of landslides in these populated regions, yet the relative importance of these human-induced factors remains poorly documented. In this work, we aim to explore the impac...

Human activity influences both the occurrence and impact of landslides in mountainous environments. Population pressure and the associated land-use changes are assumed to exacerbate landslide risk, yet there is a lack of statistical evidence to support this claim, especially in the Global South where historical records are scarce. In this work, we...

Multitemporal environmental and urban studies are essential to guide policy making to ultimately improve human wellbeing in the Global South. Land-cover products derived from historical aerial orthomosaics acquired decades ago can provide important evidence to inform longterm studies. To reduce the manual labelling effort by human experts and to sc...

Accurate and detailed multitemporal inventories of landslides and their process characterization are crucial for the evaluation of landslide hazards and the implementation of disaster risk reduction strategies in densely-populated mountainous regions. Such investigations are, however, rare in many regions of the tropical African highlands, where la...

Slow-moving landslides exhibit persistent but non-uniform motion at low rates which makes them exceptional natural laboratories to study the mechanisms that control the dynamics of unstable hillslopes. Here we leverage 4.5+ years of satellite-based radar and optical remote sensing data to quantify the kinematics of a slow-moving landslide in the tr...

Deforestation is associated with a decrease in slope stability through the alteration of hydrological and geotechnical conditions. As such, deforestation increases landslide activity over short, decadal timescales. However, over longer timescales (0.1–10 Myr) the location and timing of landsliding is controlled by the interaction between uplift and...

Lake Abaya and Lake Chamo are located within the rift valley that cuts across eastern Ethiopia. Severe soil erosion, predominantly gully erosion in the midlands and highlands, and flash flooding along rivers in the lowlands resulted in sediment and nutrient accumulation in the rift lakes. In this study, conducted in four river catchments on the Wes...

The understanding of the interplay between natural and human induced factors in the occurrence of landslides remains poorly constrained in many regions, especially in tropical Africa where data-scarcity is high. In these regions where population growth is significant and causes changes in land use/cover, the need for a sustainable management of the...

This article presents key facts and specificities on mass movement processes in regions with a tropical climate. First, the role of climate and more specifically that of rainfall characteristics is presented. Then, a focus on the link between weathering and mass movements is provided. The importance of human-induced changes is then highlighted as w...

Deforestation increases landslide activity over short, contemporary timescales. However, over longer timescales, the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered....

Historical aerial photographs provide salient information on the historical state of the landscape. The exploitation of these archives is often limited by accessibility and the time-consuming process of digitizing the analogue copies at a high resolution and processing them with a proper photogrammetric workflow. Furthermore, these data are charact...

Understanding when landslides occur and how they evolve is fundamental to grasp the dynamics of the landscapes and anticipate the dangers they can offer up. However, knowledge on the timing of the landslides remains overlooked in large parts of the world. This is particularly the case in low-capacity regions, where infrastructures are weak or absen...

Based on a literature review and two case studies, this article presents the difficulties inherent in the main disaster risk reduction conceptual models. The method used to highlight such evidence is to compare two programs on disaster risk reduction with mainstream conceptual models. The authors participated in these programs, which were confronte...

Regional landslide inventories are often prepared by several different experts, using a variety of data sources. This can result in a combination of polygon and point landslide data, characterized by different meanings, uncertainties and levels of reliability. The propagation of uncertainties due to such heterogeneous data is a relevant issue in st...

Predicting landslide occurrence is of key importance for understanding the geomorphological development of mountain environments as well as to assess the potential risk posed by landsliding to human societies in such environments. Global landslide susceptibility models use a generic model formulation to predict landslide susceptibility anywhere on...

Space-borne Differential Interferometric Synthetic Aperture Radar (DInSAR) has been extensively used in the last two decades to measure ground surface deformation, providing key information for the characterization and understanding of many natural and anthropogenic processes. However, conventional DInSAR technique measures only one component of th...

Determining rainfall thresholds for landsliding is crucial in landslide hazard evaluation and early warning system development, yet challenging in data-scarce regions. Using freely available satellite rainfall data in a reproducible automated procedure, the bootstrap-based frequentist threshold approach, coupling antecedent rainfall (AR) and landsl...

Gully erosion is a process whereby runoff water concentrates over short periods and removes the soil, sometimes to considerable depths (Poesen et al., 2003). Landslides include a range of processes by which slope material is displaced under the force of gravity (Hungr et al., 2014). Gullies and landslides play an essential role in landscape evoluti...

Studying the causes and triggers of landslides is essential to understand the key process of hillslope evolution and the hazards they generate. Such understanding is crucial in tropical areas where landslide impacts are high and on the rise, and the dearth of accurate processes characterisation is large. Here we investigate the timing and the mecha...

Rainfall threshold determination is a pressing issue in the landslide scientific community. While major improvements have been made towards more reproducible techniques for the identification of triggering conditions for landsliding, the now well-established rainfall intensity or event-duration thresholds for landsliding suffer from several limitat...

An intercomparison of seven gridded rainfall products incorporating satellite data (ARC, CHIRPS, CMORPH, PERSIANN, TAPEER, TARCAT, TMPA) is carried out over Central Africa, by evaluating them against three observed datasets: (i) the WaTFor database, consisting of 293 (monthly records) and 154 (daily records) rain gauge stations collected from globa...

Effective disaster risk reduction is often hampered by a general scarcity of reliable data collected on disastrous events, particularly in the Global South. Novel approaches are therefore necessary to alleviate this constraint, particularly with regard to reducing extensive risks. A geo-observer network, consisting of 21 reporters, was established...

Rainfall threshold determination is a pressing issue in the landslide scientific community. While main improvements have been made towards more reproducible techniques for the identification of triggering conditions for landsliding, the now well-established rainfall intensity or event – duration thresholds for landsliding suffer from several limita...

Accurate precipitation data are fundamental for understanding and mitigating the disastrous effects of many natural hazards in mountainous areas. Floods and landslides, in particular, are potentially deadly events that can be mitigated with advanced warning, but accurate forecasts require timely estimation of precipitation, which is problematic in...

The conversion of natural ecosystems into agricultural or urban areas can be accompanied by changes in geomorphological processes. This is common in areas where environmental conditions naturally predispose landscapes to landslides. Here we focus on the Ruzizi gorges, a region of the western branch of the East African Rift known for being affected...

Most landslides in Belgium, and especially the largest features, do not occur in the Ardenne, where the relief energy and the climate conditions seem most favourable. They appear in regions located mainly north of them where the lithology consists primarily of unconsolidated material. They develop on slopes that are relatively smooth, and their mag...

Over the past decades, the global exposure of persons and assets to natural hazards, like landslides, has increased faster than that their vulnerability has decreased. Therefore, the Sendai Framework for Disaster Risk Reduction (DRR) made a call in 2015 for more investment in DRR. Recent studies exposed the lack of scientific evaluation data for se...

Landslide hazard remains poorly characterized on regional and global scales. In the tropics in particular, the lack of knowledge on landslide hazard is in sharp contrast with the high landslide susceptibility of the region. Moreover, landslide hazard in the tropics is expected to increase in the future in response to growing demographic pressure an...

Landslides can lead to high impacts in less developed countries, particularly in tropical environments where a combination of intense rainfall, active tectonics, steep topography, and high population density can be found. However, the processes controlling landslide initiation and their evolution through time remains poorly understood. Here we show...

The North Tanganyika and Kivu Rift zones (Burundi, DR Congo, Rwanda) encompass a region where environmental factors such as heavy rainfall, tectonic activity, and steep topography favor the occurrence of landslides. These landslides have a negative impact on the livelihoods of the local population that suffers yearly from damage to infrastructure a...

The North Tanganyika and Kivu Rift zones (Burundi, DR Congo, Rwanda) encompass a region where environmental factors such as heavy rainfall, tectonic activity, and steep topography favor the occurrence of landslides. These landslides have a negative impact on the livelihoods of the local population that suffers yearly from damage to infrastructure a...

The international agenda for disaster risk reduction, through the Hyogo Framework for Action and the Sendai Framework for disaster risk reduction, promotes decentralised platforms as an indispensable strategy to achieve effective and efficient disaster risk management. Based on empirical data from the Rwenzori Mountains region, we question the impl...

The inhabited zone of the Ugandan Rwenzori Mountains is affected by landslides, frequently causing loss of life, damage to infrastructure and loss of livelihood. This area of ca. 1230 km² is characterized by contrasting geomorphologic, climatic and lithological patterns, resulting in different landslide types. In this study, the spatial pattern of...

The Amik Basin in the Eastern Mediterranean region occupied since 6000–7000 BC has sustained a highly variable anthropic pressure culminating during the late Roman Period when the Antioch city reached its golden age. The present 6-m-long sedimentary record of the Amik Lake occupying the central part of the Basin constrains major paleoenvironmental...

The Kanyosha watershed is unstable due to the presence of several landslides, which occupy about 3% of the study area. They are causing major damage which costs expensive to the Government of Burundi as well as to the population residing there and their properties. Roads, schools, irrigation canals, houses, crop fields, etc., are in danger of colla...

The Kanyosha watershed is unstable due to the presence of several landslides, which occupy about 3% of the study area. They are causing major damage which costs expensive to the Government of Burundi as well as to the population residing there and their properties. Roads, schools, irrigation canals, houses, crop fields, etc., are in danger of colla...

There are few data on the interactions between human factors and landslide processes in tropical environments such as those found in the mountains around Lake Kivu in DR Congo. This study focusses on the analysis of the spatial and temporal variability of natural and anthropogenic factors in and around Nyakavogo landslide (city of Bukavu). It combi...

Ground deformations in urban areas can lead to environmental constraints that must be considered in risk management and urban planning. These deformations can damage the infrastructures exposed to them. Here, the objective is to assess impacts of ground deformations on water and electricity distribution networks in the city of Bukavu (DR Congo); th...

Many cities of the South have been facing population growth for several decades. In regions sensitive to landslides, this growth can be an issue when people, often the most vulnerable, are forced to live on unstable slopes. Bukavu (DR Congo) is particularly affected by this situation. However, despite numerous slope instability in areas with very h...

Currently, there are few data on the interactions between human factors and landslide processes in tropical environments such as those found in the mountains around Lake Kivu in DR Congo. This study focusses on the analysis of the spatial and temporal variability of natural and anthropogenic factors in and around Nyakavogo landslide (city of Bukavu...

The Eastern part of DR Congo is a region naturally prone to landslides. Their impact can be important in populated areas. The objective of this research is to make a preliminary local assessment of landslide elements at risk on a recent settlement area of Bukavu (Wesha watershed). We mapped 11 landslides by combining a Pléiades image, aerial photog...

The inhabited zone of the Ugandan Rwenzori Mountains is affected by landslides, frequently causing loss of life, damage to infrastructure and loss of livelihood. This area of ca. 1,230 km² is characterized by contrasting geomorphologic, climatic and lithological patterns resulting in different landslide types. In this study, we focus on modelling t...

The Amik Basin in the Eastern Mediterranean region occupied since 6000–7000 BC has sustained a highly variable anthropic pressure culminating during the late Roman Period when the Antioch city reached its golden age. The present 6-m-long sedimentary record of the Amik Lake occupying the central part of the Basin constrains major paleoenvironmental...

In the Rwenzori Mountains, at the border between Uganda and the D.R. Congo, landslides frequently occur and cause fatalities and substantial damage to agricultural land and infrastructure. Up until recently, no information on the landslide characteristics, occurrence or spatial distribution was available. The use of archive inventories and field su...

The western branch of the East African Rift System, in Central Africa, is a region naturally prone to landslides due to the geomorphology of the area and to the occurrence of earthquakes and heavy rainfall events. The city of Bukavu (DR Congo) is located within the Rift, on the southern shore of Lake Kivu, in a tropical environment. Little is yet k...